Wells in general, and wellbores specifically, are drilled down to a formation for the purpose of producing fluid from and/or injecting a fluid into a specific subterranean formation. To complete the well for production and/or injection of fluids the wellbore is typically lined with casing that is cemented within the wellbore drilled into the earth. The casing is opened to the desired formation to allow fluid communication between the earthen formation and the wellbore. The wellbore is often further completed with another string of pipe, referred to herein as tubing, disposed within the casing to a desired formation to provide a conduit between the formation and the surface.
As is well known in the art, fluid may be produced from a formation and/or injected into a formation through the tubing string and/or the tubing-casing annulus. Often fluid is injected into the formation at a point in time and then fluid is produced from the formation through the wellbore to the surface.
In some wells casing integrity may be jeopardized due to geologic conditions such as subsidence and fault movements, or from production methods such as steam injection. Loss of casing integrity, in wells without a downhole packer, can cause uncontrolled flow, which is hazardous to personnel and the environment.
In some well designs a downhole packer is positioned within the tubing-casing annulus separating the lower portion of the annulus from the upper portion of the annulus. While this well configuration provides fluid control through the annulus, it also prevents annular injection or annular production.
There are prior art devices to provide tubing isolation, but these devices do not provide a deep annular barrier upon casing failure. Some of these devices, such as annular safety valves and subsurface surface-controlled safety valves, control the flow in the tubing string or near the surface annulus. There are also surface flow control devices such as blow-out preventers. There are devices requiring mechanically rotation of the tubing at the surface to seal the casing-tubing annulus. These devices are undesirable due to the necessity to rig up for rotation.
Therefore, it is a desire to provide a subsurface annular safety barrier to provide control of the casing-tubing annulus proximate the top of the formation in the event of loss of casing integrity. It is a further desire to provide a subsurface annular safety barrier that permits annular injection and/or annular production when the casing integrity is intact.